1. Field of the Disclosure
This disclosure relates generally to catalyst materials, and more particularly to a catalytically active material composition including a copper-manganese spinel structure as catalytically active component, and to a diesel oxidation catalyst including this catalytically active component.
2. Background Information
Operation of diesel engines and lean burn gasoline engines provide users with fuel economy and have very low emissions of gas phase hydrocarbons and carbon monoxide due to their operation at high air/fuel ratios under fuel lean conditions. The exhaust gas of diesel engines typically includes carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOX), and a relatively high oxygen content of up to 15% by volume. In addition, particulate emissions of solid soot residues, i.e., volatile organic fractions (VOF) or soluble organic fractions (SOF), originate from partially incomplete fuel combustion in the engine cylinders. The CO and HC pollutant gases may be rendered harmless by oxidation over a suitable oxidation catalyst. NO is of concern because it is believed to undergo a process known as photo-chemical smog formation, through a series of reactions in the presence of sunlight and hydrocarbons. As engine improvements are made to reduce particulates and unburned hydrocarbons on diesel engines, the NOX emissions tend to increase.
Diesel oxidation catalysts (DOC) for removal of carbon monoxide (CO), gaseous hydrocarbons (HC) and any VOF have been known and largely described in current art. Usually, platinum group metals (PGM) are used alone or in combination with other noble metals as active components in oxidation catalysts. Their ratio depends on the configuration of the exhaust gas system in which the catalyst is to be used, but noble metals catalyze different oxidation reactions in the catalyst system with different effectiveness.
Platinum (Pt) remains the most effective platinum group metal for oxidizing CO and HC in a DOC, after high temperature aging under lean conditions and in the presence of fuel sulfur. One of the major advantages of using palladium (Pd) based catalysts is the lower cost of Pd compared to Pt. However, Pd-based DOCs typically show higher light-off temperatures for oxidation of CO and HC, especially when used with HC storage materials, potentially causing a delay in HC and or CO light-off. Pd containing DOCs may poison the activity of Pt to convert paraffins and/or oxidize NO and may also make the catalyst more susceptible to sulfur poisoning. These characteristics have typically prevented the use of Pd as an oxidation catalyst in lean burn operations especially for light duty diesel applications where engine temperatures remain below 250° C. for most driving conditions.
Therefore, as emissions regulations become more stringent, there is significant interest in developing diesel oxidation catalysts with improved properties for effective utilization and particularly with improved initial activity, improved thermal stability, controlled and stable metal particle size and reduced aging. The continuing goal is to develop DOC systems including catalyst composites that provide improved light-off performance and removal of residual hydrocarbons, carbon monoxide and NOX. Additionally, as NO emission standards tighten and PGMs become scarce with small market circulation volume, constant fluctuations in price, and constant risk to stable supply, amongst others, there is an increasing need for new compositions for DOC systems which may not require PGM and may be able to maintain effective oxidation of exhaust byproducts and which may exhibit improved catalytic behavior yielding enhanced activity and performance under diesel oxidation condition. There also remains a need for methods of producing such DOC formulations using the appropriate metal loadings of non-PGM material.
According to the foregoing, there may be a need to provide catalytic properties which may significantly depend on catalytically active material compositions to obtain, under some conditions, high dispersion metal components systems for PGM-free catalyst systems which may be manufactured cost-effectively, such that performance of Zero-PGM catalysts may be improved by realizing suitable PGM-free catalytic layers in diesel oxidation catalysis.